function PasswordStrength(passwordID,strengthID)
{
  this.init(strengthID);
  var _this = this;
  document.getElementById(passwordID).onkeyup = function(){
    _this.checkStrength(this.value);
  }
};
PasswordStrength.prototype.init = function(strengthID){
  var id = document.getElementById(strengthID);
  var div = document.createElement('div');
  var strong = document.createElement('strong');
  this.oStrength = id.appendChild(div);
  this.oStrengthTxt = id.parentNode.appendChild(strong);
};
PasswordStrength.prototype.checkStrength = function (val){
  var aLvTxt = ['','低','中','高'];
  var lv = 0;
  if(val.match(/[a-z]/g)){lv++;}
  if(val.match(/[0-9]/g)){lv++;}
  if(val.match(/(.[^a-z0-9])/g)){lv++;}
  if(val.length < 6){lv=0;}
  if(lv > 3){lv=3;}
  this.oStrength.className = 'strengthLv' + lv;
  this.oStrengthTxt.innerHTML = aLvTxt[lv];
};